stripped lag screws for motor mounts

sixfootdrop · Oct 9, 2006

stripped lag screws for motor mounts

recently bought a 72 formula 23, in great condition, except that 8 of the 12 lags holding down the motor have stripped out. The drive system is unique, in that the OD is not bolted to the transom, but directly to the motor, and their is a hydraulic pump that raises and lowers the front of the motor to desired trim. My guess is that this set-up adds alot of stress to the lag bolts. Has anybody out there had this problem with this set-up? Have done research on epoxy products to fill holes and re-bolt, but am unsure if that will hold up in this situation

klos · Oct 9, 2006

Re: stripped lag screws for motor mounts

Re: stripped lag screws for motor mounts

What make/model is the engine assembly and outdrive?
Any pics? are you talking about An I/O or an outboard?

Manipulator · Oct 9, 2006

Re: stripped lag screws for motor mounts

Re: stripped lag screws for motor mounts

Welcome to my world. You have a OMC "Stinger" drive and your stringers are toast.

http://forums.iboats.com/bbBoard.cgi?a=viewthread;fid=26;gtid=1188543

strizzy · Oct 9, 2006

Re: stripped lag screws for motor mounts

Re: stripped lag screws for motor mounts

LOVE THOSE FORMULAS! Those 23's and 25's are some of the best looking boats. I havent seen omc of those OMC drives though, but it does not sound good...

Manipulator · Oct 9, 2006

Re: stripped lag screws for motor mounts

Re: stripped lag screws for motor mounts

Post some pics...do you have duals out the back?...I would love to see how they did open exhaust on a stringer.

sixfootdrop · Oct 9, 2006

Re: stripped lag screws for motor mounts

Re: stripped lag screws for motor mounts

The boat has a 350 chevy w/ an OMC outdrive. The motor mounts have been fastened to an aluminum plate (a modification) which is lagged into the stringers to disperse the load, but no matter how you slice it lags are a bad idea. Considering running stainless through-bolts through the hull and welding to a 1/4" plate on the bottom of the hull (approximately 4" x 24") on each side, and than glassing over it. What do you think?

Bondo · Oct 9, 2006

Re: stripped lag screws for motor mounts

Re: stripped lag screws for motor mounts

I think you should Strip Out the Rotten Stringers,+ Replace them...............

What you propose is a P-ss Poor Band-aid that'll Never Work...........
Atleast Not very Well,... Nor for very Long...........

Bob_VT · Oct 9, 2006

Re: stripped lag screws for motor mounts

Re: stripped lag screws for motor mounts

The stringers are the backbone. Doing the modification you planned will not work right and all you are doing is prolonging the repair.

Do it right. Replace the stringers and build them better than new.

santa666 · Oct 9, 2006

Re: stripped lag screws for motor mounts

Re: stripped lag screws for motor mounts

Yes, do it right- Do some exploritory surgery, looking for the extent of the rot. Find out how far its gone and cut the wood inside the stringers back to fresh wood (and then some)... Painful as its seems you'll have to skin back the stringers. If the wood is rotted and saturated, this will (unfortunately) be easy...

Patch in MG wood and glass, glass, glass it in.

When redoing ANY screwed in fasteners over pre drill the hole and fill it with resin. RE-drill that hole (countersunk if needed) and drive freshly resin coated stainless fasterned into the hole. back fill over the screws head with (you guessed it) catylized resin sealing it all in.

Also, you might bed a through bolted engine mount with some nice 3M 5200 taking care to watch too much on the threads, but rather making sure the 5200 is in the hole AND comes out BOTH sides.

5200 take a FULL WEEK to cure so you'll have a teeny-tiny bit of time to get the fastners adjusted to you liking...

sixfootdrop · Oct 9, 2006

Re: stripped lag screws for motor mounts

Re: stripped lag screws for motor mounts

Hi bond-o, ****-poor is not very specific, can you tell me in technical terms why through-bolting wouldn't work?
I have probed the side walls of the lag holes with a thin screw driver and it seems that the wood is in decent shape. Also I would much rather fill lag holes with resin and re-drill the lags for obvious reasons. And if indeed the stringers are in good shape would be much easier than replacing the stringers, and probably just as effective. My dilemna is this, are secure lag bolts able to withstand the force created by the motor / od combo, even in brand new stringers?

sixfootdrop · Oct 9, 2006

Re: stripped lag screws for motor mounts

Re: stripped lag screws for motor mounts

Hi Bob VT,
I am intrigued by your post to 'Build them better than new'. If I do have to replace the stringers, what would you suggest, (given the additional stress produced by this motor / OD combo?)

strizzy · Oct 9, 2006

Re: stripped lag screws for motor mounts

Re: stripped lag screws for motor mounts

It would be very helpful to have some pics of your setup, since every boat different.

I would be afraid if the wood where the lags are wasnt good enough, who say the rest of its ok? They stripped already. The wood may seem fine now, but if theres any moisture in there, its not going to last long. I had one mount that seemed ok, till I cut it open and found that it really wasnt.

Bob is talking about how when you do something, chances are you going to put a lot more time and effort into making and fixing it, resulting in a better end product. Over-kill it and dont worry about it later. Welding some studs on a plate on the outside of the boat is just asking for an array of problems stemming from many factors and really isnt in your best interest. Do it right, and you will have peace of mind when you out on the water enjoying your boat with your friends and family.

I built new motor mounts for my rig.

sixfootdrop · Oct 9, 2006

Re: stripped lag screws for motor mounts

Re: stripped lag screws for motor mounts

Hi santa 666,
I am curious about your through-bolting technique. I am assuming that you are talking about bolting through new stringers. Have you done that before with success? Also am curious what MG wood is?

strizzy · Oct 9, 2006

Re: stripped lag screws for motor mounts

Re: stripped lag screws for motor mounts

MG = Marine Grade, exterior grade coated with resin/epoxy is also fit for the job. I would perfer to use 4200 myself...

sixfootdrop · Oct 9, 2006

Re: stripped lag screws for motor mounts

Re: stripped lag screws for motor mounts

Hi strizzy,
Congratulations on your project, alot of time and effort, but hopefully worth it, as there is nothing quite like a boat on the water. I hope you are enjoying the fruits of your labor. My concern with my boat ( with the drive system unconventional in terms of additional stress on motor mounts ) is if replacing the stringers the conventional way (with lag bolts) is the prudent thing to do, or if a through-bolt assembly would be stronger.

strizzy · Oct 9, 2006

Re: stripped lag screws for motor mounts

Re: stripped lag screws for motor mounts

Thanks six!

Theres no question that through bolting would be stronger then a lag bolt in any application. I see no reason for there being a problem with rebuilt stingers and lag bolts once again, just seal the lags up this time unlike the factory did. I installed my lags, took them out, filled with resin, and then put them back in. Your boat is a 72, which is fairly old, that design worked for over 30 years, but most likely due to rotted wood, you have a small problem now. Its unlikely that too much stress on the lags caused your problem; youre not the first person to have rotted motor mounts.

Just food for thoughtwhat about something like fountain or other manufactures do and use an angle bracket off the stringers to mount to. You could through-bolt your bracket to the stringer, and then through-bolt your mounts to the bracket.

tashasdaddy · Oct 10, 2006

Re: stripped lag screws for motor mounts

Re: stripped lag screws for motor mounts

i think strizzy ment an angle bracket thru bolted to the side of the stringer,

santa666 · Oct 10, 2006

Re: stripped lag screws for motor mounts

Re: stripped lag screws for motor mounts

sixfootdrop,

Strizzy beat me to it. MG is marine grade- Do a search here and find out why its MG.

I have through bolted everything on my boat, Downriggers, lights, cupholders, fishfinder, radio... you name it it through bolted.

strizzy · Oct 10, 2006

Re: stripped lag screws for motor mounts

Re: stripped lag screws for motor mounts

Yes angle not angel! *edits post*.

Santa, not sure if you understand, but he wants to bolt through his stringers to the outside of his hull...

santa666 · Oct 10, 2006

Re: stripped lag screws for motor mounts

Re: stripped lag screws for motor mounts

Outside of his haul? Maybe HULL? I Got the joke.

and sixfootdrop- ARE YOU NUTS?!?!? DO NOT EVER try to throughbolt through your hull- DUDE! that is crazywrong!!! The only thing anyone should ever have done (by a professional) through hul is a bronze transducer, and even that should be avoided if you can.

GEEZ, you want to ruin that boat FAST huh? No, please just fix it inside the boat, We all promise It'll be:

1: Stronger.

2. Not a leaking M-f'er of a headache.

Yeah, I didn't think it was a serious post aboutthrough hull bolting

stripped lag screws for motor mounts

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